How Peptides Dissociate in Plasmonic Hot Spots

Abstract

Plasmon‐induced hot carriers enable dissociation of strong chemical bonds by visible light. This unusual chemistry has been demonstrated for several diatomic and small organic molecules. Here, the scope of plasmon‐driven photochemistry is extended to biomolecules and the reactivity of proteins and peptides in plasmonic hot spots is described. Tip‐enhanced Raman spectroscopy (TERS) is used to both drive the reactions and to monitor their products. Peptide backbone bonds are found to dissociate in the hot spot, which is reflected in the disappearance of the amide I band in the TER spectra. The observed fragmentation pathway involves nonthermal activation, presumably by dissociative capture of a plasmon‐induced hot electron. This fragmentation pathway is known from electron transfer dissociation (ETD) of peptides in gas‐phase mass spectrometry (MS), which suggests a general similarity between plasmon‐induced photochemistry and nonergodic reactions triggered by electron capture. This analogy may serve as a design principle for plasmon‐induced reactions of biomolecules.

Nanoscale structural characterization of plasmon-driven reactions

“…Although routinely observed in SERS, plasmon-driven reactivity in the tip-sample junction was mostly ignored by the TERS community. Experimental findings discussed above, as well as recently reported results from other groups, were able to transform the perception of TERS [98,99,101,[114][115][116]. These studies triggered an interest in the use of TERS for spatiotemporal characterization of plasmon-driven reactions at the nanoscale.…”

“…This question remains unclear as two contradictory pieces of experimental evidence exist. One of them suggests about the expected chaos due to extreme complexity of possibly expected reaction products [115,116], whereas the alternative evidence demonstrates the possibility of a clear readout of the sequence of biopolymers such as RNA and DNA [117][118][119] and molecular conformations on the metalized surfaces [68,76,82,83,120]. One can envision that additional experimental and theoretical studies, as well as a constructive discussion of experimental findings are required to fully understand the potential and complex nature of TERS.…”

Nanoscale Hyperspectral Imaging of Amyloid Secondary Structures in Liquid

“…No significant changes of the amide I band intensity were observed in the theoretical spectra, see the Supporting Information. Recently it has been shown that the absence of the amide I band in TER and SER spectra is mainly due to plasmon‐induced dissociation of the peptide backbone [21] . However, the increasing temperature triggers charge driven reactions because the probability of electronic transition from a vibrationally excited state (thermal excitation) is higher than from the ground state.…”

“…Recently it has been shown that the absence of the amide I band in TER and SER spectra is mainly due to plasmon-induced dissociation of the peptide backbone. [21] However, the increasing temperature triggers charge driven reactions because the probability of electronic transition from a vibrationally excited state (thermal excitation) is higher than from the ground state. Due to the liquid medium, heat dissipation from the tip is more efficient, which results in a lower effective temperature of the plasmonic structure of the surface, [22] which impedes plasmoninduced reactions.…”

Molecular Spectroscopic Markers of Abnormal Protein Aggregation

“…In particular, the most informative amide I band is absent in TER data. This problem has been broadly discussed [110][111][112], and finally it was proved that peptide backbone bonds may dissociate in the laser hot spot, which causes the lack of the amide I band. An application of the mid measurement condition (reduced laser exposition time and laser power) prevents the decomposition of the peptide backbone improving the spectra quality.…”